Daylighting and thermal loads are very important design issues for skylight design, especially in large spaces such as atria. However, the trade-off between daylighting and thermal performance of skylights hasbeen difficult to solve, due to a lack of daylighting and thermal design tools. A mathematical model was developed to predict the visible/solar transmittance, absorptance and reflectance of multi-glazed domedskylights for both direct and diffuse radiation. The model is based on tracking the beam and diffuse radiation transmission through the dome surface. Since all building-energy simulation and fenestration-rating toolsare limited to planar skylights, the model was translated into a simple method where domed skylights were substituted by optically equivalent planar skylights. The results showed that domed skylights yield slightlylower visible/solar transmittance at low sun zenith angles and substantially higher visible/solar transmittance at high sun zenith angles, or near the horizon than planar skylights having the same aperture. Absorptance ofdomed skylights is higher than that of planar skylights, particularly at high sun zenith angles, or near the horizon. The model was also compared to the IESNA transmittance calculation procedure for domed skylights and to the Wilkinson model. IESNA transmittance calculation procedure overestimates by 19% the transmittance of a dome at low sun zenith angles and significantly underestimates the transmittance of a dome at high sun zenith angles, or near the horizon. However, the Wilkinson model significantly underestimates the transmittance of a dome for both low or high sun zenith angles.
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